A developing trend in the field of wireless and radio communications is a move toward the remote radiohead (RRH) installations. In RRH installations, radio frequency (RF) transceivers are located atop radio towers and are therefore more proximate to the antennas. This reduces a cabling requirement for the transmission and reception of RF signals between the antenna and the radio head, but increases a demand for electrical power at the top of the radio tower.
For example, FIG. 1 is a schematic diagram illustrating a cellular base station 100 that includes a baseband unit (BBU) 110, a tower 120, a plurality of antennas 130 mounted thereon, and a remote radiohead unit (RRU) 140 mounted proximate to each antenna 130. A trunk cable 150 may extend from the BBU 110 to the top of the tower 120. Although not illustrated, further cables such as, for example, power and optical jumper cables may extend to the trunk cable 150 from within the BBU 110. In other words, the trunk cable 150 may be a hybrid cable. Additionally or alternatively, power and optical jumper cables may extend from the trunk cable 150 to the RRUs 140 at the top of the tower 120.
FIG. 2 illustrates in more detail a typical power distribution system 200 for (3) RRUs, which may be the RRUs 140 from FIG. 1. As illustrated, electrical equipment may be installed within the BBU 110, which may comprise an electrical cabinet having one or more circuit breakers and a power supply, here illustrated as a −48 VDC power supply. Electrically coupled with the circuit breakers are three power supply conductors 201, 202, and 203. Also provided are three ground conductors, which are illustrated as conductors having a [G] at the BBU end. These six conductors are provided via the power trunk 150 toward the RRUs 140, which are located remote from the BBU, such as near the top of tower 120. A pair of conductors (that is, a supply conductor and a return/ground conductor) carried via the power trunk 150 may be connected to a power jumper cable 160, 162, or 164. This may occur via splicing using splices 208 at a transition point 206. In other words, the six conductors of the trunk may be split into three pairs, each serving an RRU.
An installer in the field may use a screwdriver to secure the stripped conductor ends to the terminal blocks or connectors in the BBU and at the RRUs. The terminal blocks may have identifying numbers or letters and the trunk and power cables are color-coded for the specific application. These color codes may be defined by governmental agencies or by the system operator, as it may allow inspectors and technicians to quickly assess whether installations conform to specifications or local building codes. For example, power supply conductor 201 marked as [1] at the BBU end may be a cable having a red jacket, power supply conductor 202 marked as [2] at the BBU end may be a cable having a blue jacket, and power supply conductor 203 marked as [3] at the BBU end may be a cable having a brown jacket. Of course, these colors are merely examples presented herein for ease in understanding the present application and the greyscale figures. Power jumper cables 160, 162, and 164 may have commonly color-coded conductors. For example, each of the supply conductors marked as [1], [2], and [3] at the RRU end may each be a cable having a red jacket, and each of the return conductors marked as [G] at the RRU end may each be a cable having a black jacket.
The assembly consisting of the cable trunk, power jumper cables at each end, and the transitions between the trunk and cables, is typically factory-assembled. Therefore, the only modification that can be performed in the field is cutting back the trunk cable and/or power cable lengths to make them fit better in the respective cabinets or cable mounts. From an installation perspective, the current product design works well and does not present significant problems. It is desirable that no major changes be made to the installation methodologies that are currently in practice.